1. Field of the Invention
This invention relates to compound dispersions of materials and to films made from such dispersions useful in capacitor manufacture and in other applications where high dielectric constants and low dissipation factors are desired. The invention also relates to electrical capacitors made using film of the invention.
2. Summary of the Prior Art
British Pat. No. 1,030,335 published May 18, 1966 discloses that electrically conductive particles can be dispersed in a plastic matrix to improve performance of the plastic in capacitors. While carbon black is the preferred electrically conductive material and polyethylene terephthalate is the preferred plastic matrix material, the carbon black is dispersed directly into the plastic matrix to yield only a two-phase dispersion; and the carbon black must be used in such low concentrations as to assure that the carbon black particles do not make electrical contact.
U.S. Pat. No. 3,668,172 also discloses a dispersion of pigments, including carbon black, in polyethylene terephthalate. In that patent, high and low density homopolymers of ethylene are used as carriers for the pigment. However, the composition is used for spinning pigmented fibers and there is no mention of electrical properties or use of the composition in electrical applications.
U.S. Pat. No. 3,923,726 discloses pigmented blends of polyethylene terephthalate and polyolefins directed solely toward coloring the polyethylene terephthalate. U.S. Pat. Nos. 3,579,609 and 3,405,198 also disclose blends of polyethylene terephthalate and polyolefins but disclose no pigmentation.
Blends of matrix polymers and dispersed polymers are well known, with and without pigmentation. U.S. Pat. Nos. 3,435,093 and 4,010,222 disclose such blends utilizing polyethylene terephthalate as the matrix, ionomers as the dispersed polymer, and teaching that the blends can be modified by addition of pigments, fillers and so forth. U.S. Pat. No. 4,174,358 discloses blends utilizing polyamides as the matrix and a variety of modified polyolefins as the dispersed polymer. There is no disclosure that such addition of materials should be made other than to the blend; and there is no disclosure of the electrical characteristics of any of the blends.
Blends have been previously disclosed to improve the electrical properties of a film material. U.S. Pat. No. 3,585,255 discloses that ionomer blended into polyethylene terephthalate results in a material having a dielectric constant with improved stability in the face of changing temperature and other outside influences. U.S. Pat. No. 3,719,729 discloses a blend of polypropylene in polyethylene terephthalate to increase the resistance of polyethylene terephthalate to electrical breakdown. In neither of these patents is there any mention of a desire to increase the dielectric constant of the material or any teaching that a pigment should be added for any reason.
U.S. Pat. No. 3,769,260 discloses that the impact strength of polyethylene terephthalate is increased by addition, thereto, of carboxyl-terminated olefin polymers or copolymers. There is also disclosure that the strength of the material can be increased even more by addition, to the blend, of fibrous or particulate fillers including carbon and metals. Fillers, when used, are added to the blend rather than to individual components of the blend. There is no mention of electrical properties of the material, filled or not.